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Dinosaurs were not in decline when asteroid hit, study suggests

The researchers of the latest study say it is difficult to assess the diversity of dinosaurs due to gaps in the fossil record.

Dinosaurs were not in decline at the time of their extinction – which was caused by an asteroid hitting the Earth 66 million years ago, according to a new study.

The research, by the University of Bath and the Natural History Museum, contradicts previous theories and concludes that dinosaurs might have continued to dominate the planet if the impact had not occurred.

Scientists collected a set of different dinosaur family trees and used statistical modelling to assess if each of the main dinosaur groups was able to produce new species at the time.

Our data don’t currently show they were in decline, in fact some groups such as hadrosaurs and ceratopsians were thrivingJoe Bonsor

Their study, published in the journal Royal Society Open Science, found that dinosaurs were not in decline before the asteroid hit – contradicting some previous research.

It also discovered that some dinosaur groups, such as hadrosaurs and ceratopsians, were “thriving” and would not have died out then.

Lead author Joe Bonsor is undertaking his PhD jointly at the Milner Centre for Evolution at the University of Bath and the Natural History Museum.

“Previous studies done by others have used various methods to draw the conclusion that dinosaurs would have died out anyway, as they were in decline towards the end of the Cretaceous period,” he said.

“However, we show that if you expand the dataset to include more recent dinosaur family trees and a broader set of dinosaur types, the results don’t actually all point to this conclusion – in fact only about half of them do.”

Dinosaurs were widespread globally at the time of the asteroid impact, at the end of the Late Cretaceous period, and were the dominant form of animal of most land ecosystems.

It is still contentious among paleobiologists as to whether dinosaurs were declining at the time of their extinction.

The researchers of the latest study say it is difficult to assess the diversity of dinosaurs due to gaps in the fossil record.

This can be due to factors such as which bones are preserved as fossils, how accessible the fossils are in the rock to allow them to be found, and the locations where palaeontologists search for them.

In the study, the team used statistical methods to overcome these sampling biases, examining the rates of speciation of dinosaur families rather than counting the number of species belonging to the family.

“The main point of our paper is that it isn’t as simple as looking at a few trees and making a decision – the large unavoidable biases in the fossil record and lack of data can often show a decline in species, but this may not be a reflection of the reality at the time,” Mr Bonsor said.

“Our data don’t currently show they were in decline, in fact some groups such as hadrosaurs and ceratopsians were thriving and there’s no evidence to suggest they would have died out 66 million years ago had the extinction event not happened.”

The research was funded by the Leverhulme Trust and Natural History Museum.

PA


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